Patients who suffer from obstructive sleep apnea can use continuous positive airway pressure (CPAP) therapy to maintain the upper airway open while they are asleep. CPAP therapy is applied to the patient using a mask, tubing, and a flow generator. All of these components encompass the air delivery system provided to the patient.
One problem with CPAP therapy is that the flow impedance of a flow generator air delivery path results in pressure swings at the mask when the breathing load changes. As the impedance of the delivery path or the respiratory flow increases so will the observed pressure swings.
An existing solution to this problem includes reducing the inertia of the turbine or increasing peak power delivery from the power supply. These increase the ability of the system to compensate for changes in mask pressure. However, compensating for the pressure swings by adjusting the turbine pressure results in increased noise and bearing wear, and is fundamentally limited by the rate at which the turbine pressure can be changed, e.g., see U.S. Pat. No. 6,332,463.
Another existing solution to this problem includes constraining the product to have a low flow impedance delivery path, e.g., ResMed's S6 device. However, maintaining a low flow impedance of the delivery air path in a flow generator may compromise other product design goals, e.g., the turbine inlet air path being constrained to reduce radiated noise, the delivery hose being reduced in diameter, or a humidifier or filter being added to the patient circuit.
Under these conditions, it may be difficult to lower the pressure swings at the mask to clinically acceptable levels and therapy delivery may be compromised.
Thus, there is a need for an improved system that does not suffer from the above-mentioned drawbacks.